Conventionally, contact printing has been used as a system for the high speed duplication of audio and/or video signals prerecorded on a master. In contact printing, the master medium must have a coercivity three times higher than that of the copy tape. To attain high duplicating speeds, generally more than one hundred times normal speed, the master and copy are wrapped around something like a transfer drum so that the coated surfaces of each face one other. Air pressure is generally used to press the master and copy together and a bias field is applied using a stationary transfer bias head. The mirror image of the magnetic pattern on the master becomes transferred onto the copy.
Devices for printing or copying signals by tape-to-tape copying processes from a master magnetic tape on which the signals are already recorded in a mirror image to a slave or copying magnetic medium such as a tape using either a magnetic printing or thermal printing method have been described, for example, in U.S. Pat. Nos. 3,592,977; 4,755,888 and the like. Other devices for anhysteretic recording are also known for tape-to-tape copying as well as for copying from a tape to photographic film base or from magnetically recorded layers onto transparent magnetic layers on a copying substrate such as transparent magnetic layers in the cellulose acetate base of photographic film.
Currently available master tapes which provide sufficient signal to transfer a mirror image to a copy medium, particularly a photographic layer, are quite fragile. When attempts were made to record to photographic film, the commercial master failed so quickly that it was not possible to evaluate the record/playback apparatus to be used. The commercial master was brittle and had poor adhesion to base with particularly rapid failure at the edges.
To function adequately, a master must not only have high durability but it must also function without scratching or otherwise damaging the magnetic, photographic, or other layers of the copying medium. High coercivity (2000 Oe) master tapes are generally used with low coercivity (650 Oe) copy media.
Further, the master must function without "pre-exposure" of the receiving sensitized layers due to sparks from electrostatic discharge of charges accumulated during the transport and transfer processes when film webs are driven, brought together, and parted at high speed. In magnetic transfer from a master to a magnetic film base, such problems are resolved by back coating the master with a conductive layer, preferably a thin and durable conductive carbon containing layer. However, mobile components transfer from the magnetic layer and back coat on contact with the receiving medium during high speed copying. While such mobile components as well as volatile molecules or particulate debris in the air flow do not generally present a significant problem during transfer to magnetic receiving media, they are quite detrimental to a photographic layer since static changes anywhere in the system can destroy the photograhic properties of a photosensitive layer.